I was expecting that if the camera is at X:160, then all things with world coords with X:160 should be drawn at screen coords with X:160. My thinking is that effectively that means everything should be 'lined up', and that moving the camera should give the impression of them all moving away from that point at different rates.

As it stands, my code is drawing something with X:160 and xDepth:0.5 at screenX:240. I don't think that's right, but I don't know if I'm misunderstanding what should happen, my code is wrong, or if the camera is wrong :(